Processes for treating a substrate and removing resist from a substrate

ABSTRACT

The invention includes a process whereby a solvent is utilized to remove soluble portions of a resist, and subsequently the solvent can be removed with a gas-fortified liquid. In particular aspects, the gas-fortified liquid emits bubbles during the removal of the solvent. Additionally, the gas-fortified liquid can be utilized to remove residual resist scum, and in such aspects the gas-fortified liquid can emit bubbles during the scum removal.

TECHNICAL FIELD

The invention relates to processes for preparing semiconductorsubstrates, and more particularly, methods for preparing and removingresist from semiconductor substrates.

BACKGROUND OF THE INVENTION

The manufacture of integrated circuits is heavily reliant on a processknown as “photolithography.” Through photolithography, a precise mask ofphotosensitive material (photoresist) can be patterned over a substrate.The mask can be subsequently used for the fabrication of highly complexcircuits.

Photolithography typically involves the following steps. Initially, alayer of resist is formed over a substrate. A reticle is subsequentlyplaced above the resist and radiation is allowed to pass through thereticle exposing the resist to radiation in patterns defined by thereticle. Depending on whether the resist is a negative resist or apositive resist, the radiation renders exposed portions of the resistmore or less soluble in a solvent relative to unexposed portions. Thesolvent is subsequently utilized to remove the more soluble portions ofthe resist while leaving the less soluble portions as a patterned mask.A pattern can be transferred from the mask to the underlying substratewith a suitable etch.

A continuing goal of semiconductor processing is increasedminiaturization while maintaining high performance. It is known in theart that to achieve high resolution a thin layer of resist is preferred.However, a thin layer of resist typically does not withstand significantetching of the substrate material. Therefore, thicker layers of resist,or resists having high aspect ratios, are utilized, but such use createsproblems.

U.S. Pat. No. 6,451,510 to Messick, et al. describes a problem ofcollapse when using a photoresist having a high aspect ratio, and thedesirability of overcoming this adverse phenomenon. Referring to FIG. 1,a semiconductor fragment 1 is shown demonstrating the problem ofcollapse. A patterned resist 15 is layered over substrate 10. Thepatterned resist comprises vertically elongate discrete pillars, and thepillars are spaced from one another by gaps 17. A rinse 20 having a highsurface tension exists in the gaps 17 between the resist pillars.Collapse occurs as the surface tension of rinse 20 draws the resistpillars toward one another or apart from one another, whichever the casemay be. The tops of the pillars can contact one another, and sticktogether, to effectively block a gap between them.

Another problem encountered when removing resist from over a substrateis sometimes referred to as “scumming.” Scumming typically occurs whensoluble resist is not completely removed from the substrate. Residualundissolved resist remaining after development can inhibit subsequentetching of an underlying substrate. This can lead to poor resolution andless than precise substrate processing.

SUMMARY OF THE INVENTION

In one aspect, the invention includes a process for treating a substratehaving resist thereon. A gas-fortified liquid is applied to the resist.The pH of the liquid applied to the resist can be adjusted with the gas,and/or the surface tension of the liquid applied to the resist can beadjusted with the gas.

In one aspect, the invention includes a process for treating asubstrate. A resist layer is formed over the substrate. A first portionof the resist layer is exposed to radiation while a second portion ofthe resist layer is not exposed. One of the first or second portions isselectively removed relative to the other with a solvent. The solvent isremoved with a gas-fortified liquid.

In one aspect, the invention includes a process for removing residualresist from a substrate. A gas-fortified liquid is applied to theresist. The gas-fortified liquid emits bubbles. Subsequently, the liquidis removed while it continues to emit bubbles.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic cross-sectional view of a wafer fragmentdemonstrating the prior art collapse of resist.

FIG. 2 is a diagrammatic cross-sectional view of a semiconductor waferfragment at an initial processing step in accordance with an aspect ofthe invention.

FIG. 3 is a view of the FIG. 2 wafer fragment shown at a processing stepsubsequent to that of FIG. 2.

FIG. 4 is a schematic view of an apparatus that can be utilized for thepreparation of gas-fortified liquid according to one aspect of theinvention.

FIG. 5 is a view of the FIG. 2 wafer fragment shown at a processing stepsubsequent to that of FIG. 3.

FIG. 6 is a view of the FIG. 2 wafer fragment shown at a processing stepsubsequent to that of FIG. 5.

FIG. 7 is a view of the FIG. 2 wafer fragment shown at a processing stepsubsequent to that of FIG. 6.

FIG. 8 is a diagrammatic cross-sectional view of a semiconductor waferfragment at a processing step in accordance with another aspect of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention provides new processes for treating a semiconductorsubstrate with a gas-fortified liquid. In one aspect, the gas-fortifiedliquid has a surface tension and/or pH that has been altered byintroducing the gas. The gas can be introduced to the liquid prior totreating the substrate with the gas-fortified liquid and/or the gas canbe introduced to the liquid at the substrate. Carbon dioxide is a gasthat, when introduced according to the invention, alters the surfacetension and/or the pH of the liquid. An exemplary process is describedwith reference to FIGS. 2-7.

Referring to FIG. 2, a semiconductor fragment 5 is shown. Fragment 5comprises a substrate 10 having resist 15 thereon. In the context ofthis document, the term “substrate,” “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive materials, including but not limited to, bulksemiconductive materials such as semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including but not limited to, the semiconductive substrates describedabove. Further, in the context of this document, the term “layer”encompasses both the singular and the plural.

It is preferred that resist 15 is a uniform layer. Exemplary methods ofproviding this uniform layer include photoresist spinning, static spinprocesses, dynamic dispense processes, moving-arm dispense processes,and manual and automatic spinning. In the context of this document, theterm “resist” defines material which is capable of having its solubilitychanged by exposure to a suitable energy such as, by way of exampleonly, radiation, including light and ultraviolet radiation. Resist maybe referred to as “photoresist.” Resist also includes both positive andnegative resist. It is understood that negative resists are thoseresists that are soluble prior to the application of radiation.Alternatively, positive resists are those resists that are insolubleprior to the application of radiation. Either resist may be utilized invarious aspects of the invention.

FIG. 2 shows a reticle 30 over resist 15 and exposure of resist 15 toradiation 35 passing through reticle 30. Reticle 30 may also be referredto as a “photomask.” In practice reticle 30 is aligned over resist 15 toprovide a desired image upon resist 15. Passing radiation 35 throughreticle 30 results in desired portions of resist 15 being exposed toradiation while other portions of resist 15 remain unexposed. Uponexposure, one of the exposed or unexposed portions of resist 15 isrendered more soluble in a liquid solvent than the other. In thedescription that follows, the exposed portion is indicated to berendered more soluble that the unexposed portion.

Referring to FIG. 3, a wafer fragment 5 is shown after exposure to theradiation, with the gas-fortified liquid (labeled 47 in FIG. 3) utilizedto selectively remove the exposed portions relative to the unexposedportions of resist 15. The gas-fortified liquid is thus used to formgaps 46 within resist 15.

The utilization of a liquid to remove a portion of the resist subsequentto irradiation of the resist is typically referred to as development ofthe resist and the liquid used to develop the resist is typicallyreferred to as developing liquid. For purposes of this disclosure,developing liquids can include the gas-fortified liquid of the presentinvention.

Exemplary liquids which can be used during negative resist developmentinclude xylene and stoddard solvents. Exemplary liquids which can beused during positive resist development include sodium hydroxide andtetramethyl ammonium hydroxide solutions. Exemplary methods used toapply developing liquids to resist include immersion, spray and puddledevelopment. Persons having ordinary skill in the art ofphotolithography will recognize that the selection of the method used toapply liquids can be dependent on, for example, resist polarity, thefeature size, defect density considerations, the thickness of the layerto eventually be etched and desired productivity.

According to the shown aspect of the invention, gas-fortified liquid 47is utilized to remove a portion of the resist subsequent to irradiationof the resist. Additionally, or alternatively, gas-fortified liquid 47can effervesce during the development process to produce bubbles 50(only some of which are labeled). Gas-fortified liquid 47 can have a lowsurface tension. As shown in FIG. 3 meniscus 48 can be exemplary of ameniscus of a liquid having a low surface tension. As described above,the utilization of high surface tension liquids during the developmentprocess can lead to collapse of the resist. (see, e.g., FIG. 1).

Referring to FIG. 4, an exemplary apparatus 90 is illustrated which canbe utilized to produce gas-fortified liquid 47, and more particularly,to provide gas-fortified liquid 47 to a wafer treatment chamber 120.Initially a gas 100 is combined with a liquid 110 to produce thegas-fortified liquid 47. Due to the gas fortification, a gas content ofliquid 47 is increased relative to that of liquid 110. The gasfortification can, in particular aspects, alter the pH of liquid 110 toproduce a pH-adjusted liquid, and/or alter the surface tension of liquid110 to produce a surface-tension-adjusted liquid. In an aspect of theinvention, the pH-adjusted liquid has a pH less than that of the liquidprior to pH adjustment; and in an additional or alternative aspect ofthe invention, the surface-tension-adjusted liquid has a surface tensionless than that of the liquid prior to surface tension adjustment.Accordingly, a gas-fortified liquid can be a pH-adjusted liquid and/or asurface-tension-adjusted liquid. Gas-fortified liquid 47 is flowed towafer treatment chamber 120. Although FIG. 4 illustrates the applicationof gas-fortified liquid 47 to a wafer within a chamber 120, it is to beunderstood that the invention encompasses other aspects (not shown) inwhich the application is conducted without a chamber.

Exemplary gases which can be utilized to fortify the liquid are carbondioxide, ammonia and isopropyl alcohol. Carbon dioxide can be preferredbecause of its low impact on the environment. In an aspect of theinvention, gas 100 of gas-fortified liquid 47 comprises, consistsessentially of, and/or consists of carbon dioxide.

Liquid 110 can be, for example, predominantly aqueous or predominantlyorganic. For purposes of this disclosure liquids include, at least, bothdeveloping liquids and rinsing liquids. The liquid utilized inaccordance with the present invention can be free of particularcontaminants and only contain volatile contaminants, if any.

Liquids used during resist development can further include liquids usedto remove or rinse developing liquids from the resist. The utilizationof a liquid to remove or rinse developing liquids from resist subsequentto the application of the developing liquid to the resist is typicallyreferred to as rinsing of the resist and the liquid used to rinse theresist is typically referred to as rinsing liquid. An exemplary liquiduseful for rinsing positive resist includes water, and an exemplaryliquid useful for rinsing negative resist includes n-butylacetate. In anaspect of the invention liquid 110 of gas-fortified liquid 47 comprises,consists essentially of, and/or consists of water. Typically, developingliquid is removed by applying a rinse liquid in substantially the samemanner as was used to apply the liquid. For purposes of this disclosure,rinsing liquids can include the gas-fortified liquid of the presentinvention.

Referring to FIG. 5, wafer fragment 5 is shown at a processing stepafter application of the developing liquid and prior to removal of thedeveloping liquid with a rinsing liquid. The fragment comprises channels46 between resist pillars 15, and developing liquid 110 is within thechannels. Liquid 110 can be a remaining portion of a developmentsolution and remains after an exposed portion has been dissolved withinchannel 46. The liquid 110 includes meniscuses 48 within channel 46.FIG. 5 demonstrates meniscuses 48 having a relatively high surfacetension. As illustrated in FIG. 1, liquids having high surface tensionswithin resist channels may lead to collapse of the resist. According toan aspect of this invention, high surface tension development solutionscan be rinsed with a gas-fortified liquid, pH-adjusted liquid and/orsurface-tension-adjusted liquid prior to removal.

Referring to FIG. 6, wafer fragment 5 is shown at a processing stepafter addition of gas-fortified liquid 47. The fragment compriseschannels 46 between pillars 15, and gas-fortified liquid 47 within thechannels. Gas-fortified liquid 47 is shown having low surface tension tothe extent that the meniscus 48 extends upwardly. According to an aspectof the invention, gas-fortified liquid 47 can be used to rinse liquids,including developing and/or rinse liquids having high surface tensions,from resist. In accordance with an aspect of the invention, gasfortification can reduce the surface tension of a prior art liquid(e.g., liquid 20 of FIG. 1), and accordingly the prior art problem ofresist collapse (FIG. 1) is not present in the construction of FIG. 6.

Following the application of gas-fortified liquid 47 to resist 15,gas-fortified liquid 47 can be removed. Exemplary methods of removal caninclude spinning followed by thermal processing (e.g. a “hard bake”).FIG. 7 illustrates semiconductor wafer fragment 5 after removal ofgas-fortified liquid 47. As illustrated, gas-fortified liquid 47 hasbeen removed without the detrimental collapse effect described in theprior art. Preferably, the removal of gas-fortified liquid 47 leaves thecontaminant-free channel 46, as shown.

Referring to FIG. 8, wafer fragment 7 is shown at a processing stepafter developing liquid application. The fragment comprises channels 46between resist pillars 15. Liquid 110 and a foam 70 are within channels46. Bubbles 50 and paricles 75 are within liquid 110 and foam 70. Thefragment further comprises undissolved resist 60 (“scum”) proximatesubstrate 10.

According to another embodiment of the invention, undissolved resist 60(“scum”) is removed by allowing liquid 110 to effervesce during theliquid removal process. Liquid 110 may be applied to substrate 10 orresist 15 according to the methods described above. According to thisembodiment, the liquid removed from the resist may be either fortifiedas described herein, or unfortified. To allow for sufficienteffervescence during liquid removal it can be preferred to utilize agas-fortified liquid, such as that described above. Upon removal ofLiquid 110, bubbles 50 (only some of which are labeled) evolve from theliquid 110 and facilitate the migration of resist particles 75 (onlysome of which are labeled) to the upper portions of resist 15 forsubsequent removal. In one embodiment, liquid 110 effervesces to such anextent that foam 70 containing particles 75 may be generated at theupper portions of resist 15. An exemplary technique for causing liquid110 to effervesce is to utilize a vacuum chamber during applicationand/or removal of liquid 110 to reduce the gas pressure surroundingliquid 110, and thereby facilitate the emission of bubbles 50.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A process for treating a substrate comprising: providing a substratehaving resist thereon; adjusting a pH of a liquid with a gas; andapplying the pH-adjusted liquid to the resist.
 2. The process of claim 1wherein the substrate comprises monocrystalline silicon.
 3. The processof claim 2 wherein the pH-adjusted liquid has a pH less than that of theliquid prior to pH adjustment.
 4. The process of claim 3 wherein thepH-adjusted liquid is applied to the resist subsequent to the removal ofa portion of the resist.
 5. The process of claim 4 wherein the gascomprises carbon dioxide.
 6. The process of claim 5 wherein the liquidcomprises water.
 7. The process of claim 1 wherein the liquid consistsessentially of water.
 8. The process of claim 1 wherein the liquidconsists of water.
 9. The process of claim 1 wherein the gas consistsessentially of carbon dioxide.
 10. The process of claim 1 wherein thegas consists of carbon dioxide.
 11. The process of claim 1 wherein aconcentration of the gas within the pH-adjusted liquid is greater thanthe concentration of the gas within the liquid prior to pH adjustment.12. A process for treating a substrate comprising: providing a substratehaving resist thereon; adjusting the surface tension of a liquid with agas; and applying the surface-tension-adjusted liquid to the resist. 13.The process of claim 12 wherein the substrate comprises monocrystallinesilicon.
 14. The process of claim 13 wherein the surface tension of thesurface-tension-adjusted liquid is less than that of the liquid prior tosurface tension adjustment.
 15. The process of claim 14 wherein thesurface-tension-adjusted liquid is applied to the resist subsequent tothe removal of a portion of the resist.
 16. The process of claim 15wherein the gas comprises carbon dioxide.
 17. The process of claim 16wherein the liquid comprises water.
 18. The process of claim 12 whereinthe liquid consists essentially of water.
 19. The process of claim 12wherein the liquid consists of water.
 20. The process of claim 12wherein the gas consists essentially of carbon dioxide.
 21. The processof claim 12 wherein the gas consists of carbon dioxide.
 22. The processof claim 12 wherein the concentration of the gas within thesurface-tension-adjusted liquid is greater than the gas concentration ofthe liquid prior to surface tension adjustment.
 23. A process fortreating a substrate comprising: providing a substrate having resistthereon; and applying a gas-fortified liquid to the resist.
 24. Theprocess of claim 23 wherein the substrate comprises monocrystallinesilicon.
 25. The process of claim 24 wherein the gas-fortified liquid isapplied to the resist subsequent to removal of a portion of the resist.26. The process of claim 25 wherein the gas of the gas-fortified liquidcomprises carbon dioxide.
 27. The process of claim 26 wherein the liquidof the gas-fortified liquid comprises water.
 28. The process of claim 23wherein the liquid of the gas-fortified liquid consists essentially ofwater.
 29. The process of claim 23 wherein the liquid of thegas-fortified liquid consists of water.
 30. The process of claim 23wherein the gas of the gas-fortified liquid consists essentially ofcarbon dioxide.
 31. The process of claim 23 wherein the gas of thegas-fortified liquid consists of carbon dioxide.
 32. A process forrinsing a resist having channels therein, comprising: providing a resistsupported by a substrate, wherein channels extend into the resist; andrinsing the resist with a gas-fortified liquid.
 33. The process of claim32 wherein the substrate comprises monocrystalline silicon.
 34. Theprocess of claim 33 wherein the gas of the gas-fortified liquidcomprises carbon dioxide.
 35. The process of claim 32 wherein the gas ofthe gas-fortified liquid consists essentially of carbon dioxide.
 36. Theprocess of claim 32 wherein the gas of the gas-fortified liquid consistsof carbon dioxide.
 37. The process of claim 32 wherein the liquid of thegas-fortified liquid comprises water.
 38. The process of claim 32wherein the liquid of the gas-fortified liquid consists essentially ofwater.
 39. The process of claim 32 wherein the liquid of thegas-fortified liquid consists of water.
 40. A process for treating asubstrate comprising: providing a substrate having resist thereon; andapplying an effervescent liquid thereto.
 41. The process of claim 40wherein the substrate comprises monocrystalline silicon.
 42. The processof claim 41 wherein the effervescent liquid is applied to the resistsubsequent to the removal of at least a portion of the resist.
 43. Theprocess of claim 42 wherein the liquid of the effervescent liquidcomprises water.
 44. The process of claim 43 wherein the effervescentliquid emits a gas comprising carbon dioxide.
 45. A process for treatinga semiconductor substrate comprising; providing a semiconductorsubstrate having liquid thereon; and removing the liquid from thesubstrate as bubbles of a gas are emitted from the liquid.
 46. Theprocess of claim 45 wherein the semiconductor substrate comprisesmonocrystalline silicon.
 47. The process of claim 46 wherein thesemiconductor substrate includes a layer of resist.
 48. The process ofclaim 47 wherein the liquid comprises water.
 49. The process of claim 48wherein the gas comprises carbon dioxide.
 50. The process of claim 45wherein the gas consists essentially of carbon dioxide.
 51. The processof claim 45 wherein the gas consists of carbon dioxide.
 52. The processof claim 45 wherein the liquid consists essentially of water.
 53. Theprocess of claim 45 wherein the liquid consists of water.
 54. A processfor treating a semiconductor substrate comprising: providing asemiconductor substrate; forming a resist layer on the semiconductorsubstrate; exposing a first portion of the resist layer to radiationwhile not exposing a second portion of the resist layer; selectivelyremoving one of the first or the second portions relative to the otherof the first and second portions with a solvent, thereby forming apatterned resist; and removing the solvent with a liquid, wherein theliquid has been fortified with a gas.
 55. A process according to claim54 wherein the semiconductor substrate comprises monocrystallinesilicon.
 56. A process according to claim 55 wherein the liquidcomprises water.
 57. A process according to claim 56 wherein the gascomprises carbon dioxide.
 58. A process according to claim 54 whereinthe gas consists essentially of carbon dioxide.
 59. A process accordingto claim 54 wherein the gas consists of carbon dioxide.
 60. A processaccording to claim 54 wherein the liquid consists essentially of water.61. A process according to claim 54 wherein the liquid consists ofwater.
 62. A process for treating a semiconductor substrate comprising:providing a semiconductor substrate comprising monocrystalline silicon;forming a resist layer on the semiconductor substrate; exposing a firstportion of the resist layer to radiation while not exposing a secondportion of the resist layer; selectively removing one of the first orthe second portions relative to the other of the first and secondportions with a solvent thereby forming a patterned resist; and removingthe solvent with water, wherein the water has been fortified with carbondioxide.
 63. A process according to claim 62 wherein the water emitscarbon dioxide while removing the solvent.